Republican presidential candidate Donald Trump speaks during a news conference, Saturday, July 25, 2015, in Oskaloosa, Iowa.
AP
A lot of Republicans would like Donald Trump to go away. But not too far.

The prospect that Trump might eventually leave the primaries and run for president on his own has started to cast a shadow on the race, reviving memories of Ross Perot, Ralph Nader and the chills their third-party campaigns gave to Republicans and Democrats in turn.

Not all Republicans foresee the apocalypse if Trump goes rogue. But they're worried just the same. The party's best bet may be to see him ground down in the GOP contest with the hope his supporters will disperse to others in the field. Trump calls an independent run "highly unlikely" but it depends "how well I'm treated" by party leaders.

Here are five things to consider as Trump refuses to rule out a third-party effort.

WHERE'S HE STAND?

Republican presidential candidate Donald Trump speaks at a rally and picnic, Saturday, July 25, 2015, in Oskaloosa, Iowa.
AP
Polls this soon in the contest can be good at finding flavor-of-the-month favorites, not at judging who's got staying power. The almost universal expectation is that Trump will sink from his lofty poll heights as first-blush sensations have done in the past: Michele Bachmann and Rick Perry to name just two.

Yet the polls this time are more than fingers in a fickle wind. They determine the 10, out of 16, who will attend the first debate on Aug. 6. Trump is surely in.

As a billionaire who is paying for his campaign and not beholden to donors, Trump is also uniquely positioned to control his own staying power. He appears to have the money to take his campaign through the primaries no matter how he performs in early contests — or to mount a hugely expensive third-party effort instead.

On this question, exasperation with Trump is palpable among some activists on the ground. Former Iowa Republican Chairman Matt Strawn says: "It is a fool's errand to try and predict Mr. Trump's behavior. That being said, Mr. Trump needs to be honest with Iowans, Iowa Republicans — if he is seeking the nomination exclusively as a Republican or if he'll take his ball and go home if Iowa Republicans decide on someone else."

HOW REPUBLICAN IS TRUMP, REALLY?

Donald Trump (seated L) and his wife Melania (seated R) are applauded before a dinner hosted by the Sarasota Republican Party honoring him as Statesman of the Year in Sarasota, Florida August 26, 2012.
REUTERS/Mike Carlson
Very Republican on tax cuts and various other economic policies; not so Republican on health care, some social issues and more.

He once favored a single-payer health care system, a big step beyond President Barack Obama's health care law and one that put him in the company of Vermont Sen. Bernie Sanders, the socialist challenging Clinton for the Democratic nomination. He's likewise critical of free-trade agreements.

Perhaps more on point, Trump has donated heavily to both parties over the years. Records show he has only given money to Republicans since 2010. Before that, one of the preferred candidates for his largesse was Hillary Clinton, who came to his third wedding in 2005. (Trump now calls her the worst secretary of state ever.)

THE PEROT-NADER EFFECT

Independent presidential candidate Ralph Nader on Wall Street across from the New York Stock Exchange, October 16, 2008.
REUTERS/Brendan McDermid
The odds are heavily stacked against an independent becoming president. But those who try can change the dynamic of a race — and history.

In the incredibly close 2000 election, Nader won less than 3 percent of the popular vote and no states. But the liberal is widely considered to have tipped Florida and perhaps New Hampshire to Republican George W. Bush. Either state would have given Democrat Al Gore the presidency.

Bush was affirmed the winner in Florida by 537 votes. More than 22,000 Floridians voted for Nader and exit polls indicated 47 percent would have voted for Gore and only 21 percent for Bush if Nader had not been a choice.

In 1992, Perot spent about $64 million of his fortune to get his name on ballots across the country, a struggle for anyone outside the two-party system. He won an impressive 19 percent of the popular vote, though no states, as Democrat Bill Clinton defeated the incumbent President George H.W. Bush.

Perot drew support from both parties and from people who might not have voted normally. There is no consensus that he cost Bush the election. But many Republicans believe Bush suffered from Perot's participation.

GOP pollster Kellyanne Conway says if Trump runs on his own, "no one's voters are completely safe" because he could tap into anti-establishment sentiment in both parties.

But Democratic strategist Cardona argues that if he runs independently: "I think right then and there we can celebrate that Hillary Clinton will be the next president."

WHAT'S IT TAKE?

Miss Universe 2013 Gabriela Isler, from Venezuela, left, and pageant owner Donald Trump, of the United States, point to each other while posing for a photo after the 2013 Miss Universe pageant in Moscow, Russia, on Saturday, Nov. 9, 2013.
AP Photo/Ivan Sekretarev
It takes a lot of money to make a consequential independent run for the White House. Trump seems to have it, although the extent of his fortune is not public and it's not known how much he would be willing to spend.

Malek estimates the cost of a serious third-party campaign at $500 million and doubts Trump would plow that much into an outside effort. "He's a businessman who will look at his potential for winning and decide it will be a poor return on his investment," Malek predicted.

Luntz puts the cost at $200 million. "Trump can write that check today without going around raising money. What's more, the fact that he's not bankrolled by special interests and lobbyists is a very powerful message in today's environment."

WHAT'S TRUMP SAY?

Republican presidential candidate Donald Trump speaks at FreedomFest, Saturday, July 11, 2015, in Las Vegas.
AP
— "No. I won't go on record as saying that." July 18, on whether he would rule out a third-party bid.

— "Absolutely, if they're not fair, that would be a factor." July 22, telling The Hill newspaper an outside bid is an option if the party mistreats him.

—"I want to run as a Republican. I think I'll get the nomination." July 23.

—"It's highly unlikely" he'll run on his own, depends on "how well I'm treated." July 25.

—"If I'm treated fairly and I get a good, fair shot at this, and I'm not, you know, being sabotaged with all sorts of nonsense and a lot of phony ads ... I would have no interest in doing that whatsoever. All I want to do is be treated fairly." July 27.